This comment came up the last time I was in a state on the east coast with remarkably complicated and badly documented rules for contractors*. In some cases, contractors buy for resale, in other cases they pay tax on their product but charge tax on their services; and in other cases they can sell their services for resale, but only if they get a certificate that the state doesn't seem to want to tell them the number of.
Every time I do seminars in this state I cringe, because the contractors in the room, who would like to do the right thing, can't seem to figure anything out. And neither can I.
One participant speculated that the state deliberately kept things confusing so that they were assured, whenever they audited contractors, that they'd find plenty of money to assess.
I'd hate to believe that were true.
Sales Tax Guy
* I don't need trouble with these people, so I won't mention the state. But trust me, if you're a contractor and you're in this state, you know who I'm talking about.